The present invention is directed toward a multi-stage water filter and, more particularly, to a system for treating polluted air by impinging the air against a liquid surface, causing the air and liquid to mix and thereafter separating the air from the liquid several times, thereby ensuring high quality cleaning.
Most portable vacuum cleaners have two main units: a fan for suctioning polluted air and some system for cleaning the air of various particles and dust, typically a filter. Portable vacuum cleaners used in households for cleaning carpets, upholstered furniture, bare floors, walls, etc., are characterized by two main features: the ability to suction, i.e., the maximum weight of particles that may be suctioned, and the ability of the filter unit to retain all of the various particles. The ability to suction depends on the velocity of air flow entering the machine. The air flow is what captures all the loose particles from a surface and suctions them into the machine. The velocity of the air flow, other than the power of the motor and the design of the fan, depends on the resistance it meets inside the machine from the entryway to the exit.
Household cleaner filters are typically bags made from paper or fabric and are the most commonly used for cleaning the contaminated air from particulate matter (Consumer Reports: Vacuum Cleaners 1995; Mody, Jakhete Dust Control Handbook Pollution Technology Review #161, Noyes Data Corporation.) Other types of filters are cyclones and liquid filter systems.
Bags, as elements for catching dust have one well known disadvantage. That is, the smaller the pores in the bag, the finer the dirt particles they are able to catch. However, this creates a greater resistance against the exiting air flow which slows it and reduces the vacuum cleaner's suction ability. Furthermore, it is impossible to catch every particle of dust with a filter bag since only a nonporous bag will catch every particle, which is what eventually becomes of the bag once it is clogged, therefore completely stopping the air flow which catches the particles. It should also be noted that all particles that are suctioned in and not retained are released back into the environment. The smaller the particles, the more dangerous they are to humans.
Cyclones are inertial collectors which transform a gas stream into a confined vortex, from which inertia moves suspended particles to the wall of the cyclone's body. Cyclones have a significantly lesser resistance than bags, but they can only capture particles larger than 5 microns (1992 ASHRAE Handbook for Heating, Ventilating, and Air Conditioning System and Equipment, SI Edition, p. 26.7.) In FANTOM vacuum cleaner machines disclosed in U.S. Pat. Nos. 4,573,236; 4,643,748; 4,826,515; 4,853,008; 5,078,761; 5,145,499; and 5,160,356, a common porous filter is used to seize particles smaller than 5 microns but these filters have the same disadvantages as filter bags, discussed above.
Wet scrubbers and water filters used for air cleaning exist in two varieties. The first has a continuous feeding of water into the stream of contaminated air and a constant removing of the sludge. The second has a periodic feeding of water and a periodic removal of the sludge. Portable household cleaners usually use the second type. Water can capture finer particles, as small as 0.3 micron. However, these particles can only be captured by passing the contaminated air through liquid (1992 ASHRAE Handbook for Heating, Ventilating, and Air Conditioning System and Equipment, SI Edition p. 26.15). Furthermore, water filtration has a lesser resistance to the air flow than bags or other filters.
The vacuum cleaner "Rainbow" (Rexair, Inc.) is described in U.S. Pat. Nos. 2,221,572; 2,228,750; 2,886,127; 2,945,553; 4,640,697; and 4,824,333. This machine basically consists of a water basin, an electrical motor which drives a system of centrifugal fans suctioning in the contaminated air into the water basin, and a spinning separator which separates clean air from the water. A spinning hollow cone-shaped cup with slits on the sides perpendicular to the direction of rotation is used as a separator. The same motor that drives the fan system functions as the drive for the spinning separator. The contaminated air enters the water basin through a nozzle directed perpendicularly to the surface of the water.
This Rainbow device, however, has a number of disadvantages. First, it results in a low quality of air cleaning due to poor mixing of the contaminated air and water since the shortest path from the nozzle to the separator is by avoiding the water surface altogether, and because the air suctioned in has a low kinetic energy and a low impulse of force. If the nozzle end is placed lower than the water surface, an evacuation of air above the water surface occurs and the whole mass of water goes into the separator which cannot possibly separate it from the air. Consequently, many of the later filed "Rainbow" patents include an above-the-surface nozzle. According to "Consumer Reports," 1995, Rainbow holds the finest dust, like household dirt, well, but cannot catch most mineral particles which are not easily wetted, and therefore emits them into the air again.
Secondly, the mechanically rotating separator requires a complicated mechanical drive and is unreliable because of the large number of parts rotating at great speeds. Other than that, wet or damp dust, and other various debris, sticks to the separator clogging its slits.
In addition, the spinning slotted separator of the Rainbow vacuum cleaner has a relatively high aerodynamic resistance lowering the suctioning ability of the vacuum cleaner.